| B-type wheat starch is the byproduct of A-type wheat starch and gluten flour production.It can bind tightly to protein, which hinders its further processing and utilization. In this study,using the B-type wheat starch as a raw material, caramel pigment was prepared by theMaillard reaction between reducing sugar and amino compounds or ammonia-basedcompounds, and Caramel reaction of micromolecule sugar. The efficient and low-energymethods for caramel pigment preparation from the B-type wheat starch were developed. Amethod was to prepare caramel pigment through hydrolysis of B-type wheat starch bymicrowave radiation and acid. The other method was to prepare caramel pigment byextruding B-type wheat starch directly. Using the two methods, the product quality andprocess feasibilities of caramel pigments preparation were compared. In addition, the factorsinfluencing the contents of harmful4-Methylimidazole (4-MeI) in the caramel pigments,were investigated. Finally, the effects of antioxidants on the acrylamide contents in theproducts were examined to enhance the food safety of caramel pigments. The results are asfollows:(1) In the reaction using microwave radiation and acid, sodium chloride, potassiumchloride, ferric chloride, and magnesium chloride could promote the hydrolyzation of theB-type wheat starch, and reduce acid consumption significantly. These metal salts in thehydrolysate could affect the production of caramel pigment, sodium chloride, potassiumchloride, and ferric chloride could promote the browning reaction; ferric chloride had themost significant catalytic action. However, caramel pigment had poor tolerance to salt. Thesodium chloride promoted the browning reaction obviously, and the corresponding caramelpigment had a better resistance to salt and acid. For the0.05%hydrochloric acid solutioncontaining sodium chloride, moderate heat radiation (580w of microwave output power) for8min resulted in the DE value of the hydrolysate at79.86%. Compared with the conventionalprocess using heat treatment, the B-type wheat starch could be hydrolyzed more thoroughlyunder the microwave irradiation, and the reaction rate could be enhanced significantly.(2) The mechanisms about the effects of amino compounds on the color intensity ofcaramel pigment were discussed preliminarily. Compared to the strong acid ammonium salts(such as ammonia sulfate, ammonia chloride), the weak acid ammonium salts (such asammonium acetate, ammonium carbonate) could make the Maillard reaction of reducingsugars more easily. During heating, the anion of different ammonium salts had differentinfluence on the glucose structure. Ammonia chloride could not change the glucose structure,while the ammonia sulfate, ammonium carbonate, and ammonium biphosphate changed thestructure of partial glucose and generated the sugars, which could cause non-enzymatic browning reaction more easily. As a result, the color intensity of caramel pigment wasimproved to a certain degree. The relationship between reaction time and the color intensityof caramel pigment prepared from9kinds of amino compounds or ammonia-basedcompounds and hydrolysates of B-type wheat starch was investigated. It was found that thecaramel pigments from ammonium carbonate and the B-type wheat starch hydrolyzates haverelative high color intensity and stable properties.(3) The B-type wheat starch contained77.31%starch and4.23%protein, and needed toadd amino compounds to the hydrolysate to promote the Maillard reaction. Comprehensiveconsideration of the effect of the ammonium carbonate level on the color intensity and safetyof the caramel pigment, the adding amount of the ammonium carbonate was5%(m/m). Onthe basis of single factor experiment, the response surface analysis of three factors and threelevels was used to process parameters optimization of preparation of the caramel pigmentfrom the hydrolyzates. The optimum reaction conditions were as follows: the mass fraction ofthe B-type wheat starch hydrolyzates was50%, and the reaction time and temperature were82min and146oC respectively. Under these conditions, the preparation of the color intensityof the caramel pigment (I) was76053EBC units.(4) The microwave radiation acid process should dilution first and then concentrationduring preparing the caramel pigment by hydrolyzing the B-type wheat starch. Thus, thismethod should consume more energy. However, producting of caramel pigment by extrudingthe B-type wheat starch directly could cover this shortage. Compared with the single screwextruder, the twin screw extruder was suitable for producing caramel pigment because of thecharacteristics of good mixing, self-cleaning and forward delivery. The ideal extrusionconditions were founded through comparative tests and response surface analysis method.Thus, the amount of sulfuric acid, water and amino compounds (based on the NH3) were18mL,120mL and40g per kg wheat B-starch, respectively. The color ratio was20338EBCunits while the extrudate was prepared under conditions as follows: feed rate1.7kg/min,screw speed150r/min, barrel temperature of region I70oC, barrel temperature of region II140oC, barrel temperature of region III215oC. The reasons for low color ratio of caramelpigments produced by extrusion were short dwell time of materials, low degree of starchdegradation and inadequacy of chemical reactions which were founded by analysis of theeffects on the color ratio of the different compositions of B-type wheat starch hydrolysates.Furthermore, the addition of insulation measures of the subsequent treatment lead toimproving color ratio of the caramel pigments. As a result, the color ratio of caramel pigment(II) could be increased to50263EBC units while incubating at180oC for16min.(5) Both caramel pigment (I) and (II) were in line with the GB8817-2001. Two kinds ofthe caramel pigments were all positively charged and belonged to the brewing caramelpigment. And the pHs were4.28and3.91, respectively. The color ratio, coloring property and salt tolerance of the caramel pigment (I) were better than that of the caramel pigment (II). Theacid resistances of both caramel pigments were fine, and the UV-visible spectra werebasically identical, the maximum absorption spectra were both270nm. However, the caramelpigment (I) was fit for adding to soy sauce and vinegar while caramel pigment (II) wassuitable for vinegar coloring.(6) The caramel pigment, produced by extruding B-type wheat starch directly, was insolid form. The process was simpleness, low energy consumption, continuous and highefficiency, since the hydrolyzation and browning reaction of the B-type wheat starch occurredsimultaneously. However, for the residence time of the materials in the extruder was short,the level of the reaction was insufficient, which caused the color index of caramel pigment (II)lower than caramel pigment (I), so as the dyeing test. Furthermore, the high-temperature,high-pressure, acid materials in the extruder corrupting the metallic iron of cylinder inwalland screw surface might generate iron ions, which lead caramel pigment (II) lower salttolerance. Thus, caramel pigments with excellent quality could be produced by extruder if thestructure parameters and the corrosion resistance of the equipment were improved, and theresidence time of the materials in the extruder was prolonged.(7) The dosage of ammonium carbonate had a great impact on the content of4-MeI inthe caramel pigment. When the amount of ammonium carbonate was6.0%, the4-MeI contentin the product exceeded a predetermined GB8817-2001index which was not greater than0.02%(converted to the value of OD610=0.1) under the experimental conditions (reactiontemperature140oC, reaction time70min). The reaction temperature and the mass fraction ofB-type wheat starch hydrolyzate also affected the content of4-MeI in the caramel pigment.The4-MeI content increased rapidly as the temperature rose to160oC, while the content of4-MeI was at the minimum value when the mass fraction of B-type wheat starch hydrolyzatewas50%. The4-MeI had been produced during the initial stage of the Maillard reaction andthe converted content of4-MeI became higher in that the color intensity of the caramelpigment showed lower. As the reaction proceeding, the increasing rate of4-MeI contentbecame more slow, and the content of4-MeI dropped significantly after conversion while thecolor intensity of the reactants increased rapidly.(8) A mixture of glucose and ammonia was allowed to react at120°C for60min in thepresence of ascorbic acid at final concentrations of0to0.08M. The caramel pigmentsobtained from these reactions were all positively charged. As the concentration of ascorbicacid increased, the color intensity of the caramel pigment showed a decreasing trend, whilethe intensity of the fluorescence and total amount of pyrazines in the volatiles showed atendency to increase. The addition of ascorbic acid did not result in obvious changes in theUV-visible spectra of the ammonia caramels and the types of pyrazines in the volatiles werealso unchanged. It is noteworthy that the addition of0.02to0.08M ascorbic acid did reduce the formation of the by-product acrylamide, a harmful substance in food. When theconcentration of ascorbic acid added reached0.04M, the content of acrylamide in thecaramel pigment was20.53μg/L, which was approximately44%lower than that withoutascorbic acid. As a result, ascorbic acid can be considered to improve the quality and safetyof caramel pigments. |
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